In aircraft, cable control systems are commonly used to direct pilot maneuvers to the ailerons, elevator, and/or rudder. Thermal instabilities are present in aircraft due to the variation of temperatures as the aircraft travel at various altitudes, and thermal instabilities between the cables of the cable control is systems and the surrounding structure have been addressed by incorporating devices known as thermal compensators. Prior-art thermal compensators use mechanisms (e.g., with springs) to react to thermal instabilities, and hence maintain a relatively stable tension in the cables of the cable control systems. Shortcomings of such devices are cost, weight and sensitivity to application.
U.S. Pat. No. 2,409,800, issued on Oct. 22, 1946 to Rockafellow, discloses a temperature change compensating apparatus. This apparatus uses a scissoring mechanism to apply scissoring forces on a cable of a cable control system. The scissoring forces are induced by the change of length of a cable and pulley assembly, resulting from thermal variations. The cable pulls on the scissoring mechanism.
The apparatus of Rockafellow is voluminous, and therefore adds a non-negligible amount of weight to the vehicle using same. It does not offer the possibility of using some existing components of the cable control system.
Considering that aircraft now commonly incorporate different types of materials that do not react similarly to thermal variations, such as composite materials and metallic components, there results an increase in thermal instabilities between materials that are used in broad temperature ranges. Using the above example, composite material specifically has a small coefficient of thermal expansion, while high-strength lightweight alloys have medium to large coefficients, thereby causing different expansions and contractions, which may enhance thermal instabilities.